Telegraph system provided with channel assurance and transmission regulation



2 Sheets-Sheet l I Apnl 13, 1948. E. PRAIZNER TELEGRAPH SYSTEM PROVIDED WITH CHANNEL ASSURANCE AND TRANSMISSION REGULATION Filed Feb. 25, 1944 l l I h v. Wm W3 w! H rm M M I Q3 MN m s I my r 5:1 A M N |ll E w y a B .33 32: vol

April 13, 1948. E. PRAIZNER 2,439,398

' TELEGRAPH SYSTEM PROVIDED WITH CHANNEL ASSURANCE AND TRANSMISSION REGULATION Filed Feb. 25, 1944 2 Shaets-Sheet 2 'lvm sn'z. COIVTHCT I POWER SWITCH INVENTOR 5 PRA/ZNER A r TORNEV Patented Apr. 13, 1948 TELEGRAPH SYSTEM PROVIDED WITH CHANNEL ASSURANCE AND TRANS- MISSION REGULATION Edward Praizner, Montclair, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application February 25, 1944, Serial No. 523,816

This invention relates to an intercommunicating teletypewriter system, and more particularly to testing and alarm circuits for use therewith.

An object of the invention is to indicate to an attendant at one of a plurality of interconnected stations, by means of visual and/or audible alarms, whenever the system conditioned for operation fails to function in a satisfactory manner.

In a so-called half duplex arrangement in which operators at each terminus of a channel transmit by means of a keyboard and receive by means of either a printer or a printing reperforator, the operators take care of situations which result, in general, in simultaneous breaking or garbling of both operators transmission. However, in a half duplex system with machine or automatic sending and either reperforator or printer receiving, the machine senders are unable to make immediate acknowledgement of'messages 33 Claims. (01. 178-2) or request resending. They also lack the ability (except as they are manipulated by attendants) possessed by operators to resend the part of a message lost as a result of a break signal, or, in general, to recognize that they are sending to an open line or to a station ineffective to receive, or except in case special break mechanism is provided, to recognize that the opposite station is at the time sending. These and other conditions have resulted in lost messages or parts of messages.

Therefore, an object of the invention is to prevent such undesired occurrences and to provide half duplex or equivalent channels of transmission and especially those provided with machine senders with equipment in part functioning in lieu of the intelligence of operators, by preventing sending where no sending should occur and by directing the attention of attending personnel to untoward circuit or apparatus conditions. In short, there is greater assurance of an operative circuit and such equipment may be styled circuit assurance equipment. From another aspect, the automatic equipment may be considered as keeping a constant watch upon the channel of transmission in the same manner as would the operator of a keyboard machine upon the channel giving her full attention to that channel.

From a generic standpoint, the object of the invention is to provide assurance against loss of messages by unobserved circuit failure.

According to the present invention an intercommum'cating teletypewriter system is equipped with testing facilities automatically operable whenever (1) the line circuit interconnecting two stations and normally energized, is conditioned for operation, and (2) a connection established for message communication is discontinued and the system does not restore to its normal, idle condition wherein the line is energized and the interconnected stations are conditioned for operation and testing. This idle condition is also referred to herein as usable or closed. condition. The testing facilities form a part of the normally energized line circuit and are directly operable by pulses therein, the effective pulses for operating the alarm equipment being, at least, slightly longer in duration than a teletypewriter character signal combination.

Among the features of the present invention is the provision of equipment for automatically indicating by visual and audible alarm signals (1) when a message is sent from one of the interconnected stations and not received at a remote station connected thereto, at which time the transmitter-distributor at the sending station automatically becomes disabled, (2) when the line circuit in its idle but usable condition fails, (3) when the power, or start, switch at a receiving station is not in its on position at the time the corresponding switch at the sending station is in its "on position, (4) when the power switch at one station is operated to its off position, say at the close of a days business, and the .cor-

responding switch at another station connected in the system is not restored to its off position, (5) when a power switch at one of the interconnected stations is inadvertently operated to its off position during the course of a days business, (6) when during transmission of a message any major electrical or mechanical difliculty occurs to affect the reception of the message at which time the transmitter-distributor at the sending station automatically becomes disabled.

Another feature is the provision for preventing simultaneous sending from the stations at opposite ends of the interconnecting line circuit.

Another feature is the provision whereby after a call is initiated and no message transmitted, the interconnected stations of the system alternately have access to the interconnecting line for the purpose of transmission, each for a timed period during which period the transmitting device at the other station of those interconnected, is prevented from transmitting but the receiving device thereat can receive.

Another feature is the provision whereby either of the interconnected stations is prevented from sending messages when the other station for which the'message is intended is unable to rethe detailed description hereinafter fo'llowi-ng when read in connection withthe accompanying drawings wherein:

Figs. 1 and 2 represent an intercommunicating teletypewriter system. Fig. 1 shows station A and Fi ;2 shows on QB t e stations b i g interc nne te y normally-z I SB EIi IELCi FGH-it ineludinga single" line "regenerative repeater, at one or more; intermediate-points.

Refe n toFia, lr ta ion Ancmprises aty ing-reperforator Hi I, for, receiving;-messages-both incoming and-ou oing .atationsn bvz tin and per orat n -;b.0t: th :ztransm tt and i the receiv d; messa esxon tape 02 and :a ansmitterdistributor not for trans-lating outgoin :message signal combinationsof aseco dztaDets ch-a p m3, into, codedgsigna current-combinations:for

transmission over the :five selective segmentsqof a start-stop rotary distributor;|;l}5,5to ;c-onductor I106 of; the normally closed; l;ine eirci;1it extending r :to .stationB. The :tYping-neperforator; I11 I :;may be of the type disclosed; in C. =S-wan, :United States Patent;2,3,08,5.54, issued January: 19, .1943,

.and the transmitter-distributor: tMmaybc .of. the type disclosed in :Wfatson, "United -States :Patent 2,055,567, issued Se.ptemberi;29,c1-9? 6. ;The

translated signalcombinations; at station ".A. are

. also transmitted over conductor Ll 09 forscausing the. operation of. printer magnet -'l-r'IRzprovided for operating: typing-reperforator it!) I tOrDIOdHCB a home, or local, copy of the message transmitted to station 13. 1

Tape l03inay leadfrom a keyboardoperated -periOrator (not .shown) or from;.a.-reperforator (not shown) operatedunder controlc-ofleagl-ine I (notshown) incoming tostation A. orr-itmayzbe suppliedmanually .with. pieces of tape perforated with messages tobe sent. Usually;-howeverpthe tape H33 will extend froma .perforator or reperforatordirectly to -the sensing head of .the transmitter and tapestop. arm: I61 -.will stop; the transmitter distributor 04 whenithe tape becomes taut. arranged in a similar. manner. The '7 transmitter- :distributors m4 and :204are considered totypify Corresponding elements of station Bare any type of machine transmitters including those which have mechanical distributors well as those which have segmental. distributors.

Distributor [05,sin its idle condition,-connects conductor. [136* to: a circuit; extending-over its inner ring, brushes and-stop segment, conductors I01 7 and 1 [(89, through the: lower winding of repeater relay I-'-L, conductor .1: I 0, iback contact :and

upper armature ofrrelay:I.f+OL, to, gro1mded ne ..ative battery H'l Relay l.-:L is; one ,of twopolarized relays, the other being relay lhl, which are alternately operated :in -;response to signals incoming and outgoing over the line circuit.

Power, or start, switch .zHaZ serves :to start, 'in

operation, .motor .I. Is :for transmittendistributor .234 may -.be :of the type disclosed in Watson I04 and motor H4 for typing-reperforator lfil as well as the station equipment at each of stations A and B. The operation of the station equipment is effective to make the ready-for-service test at each station in response to the operation of ,the-power-switch at either of the stations. So-

called stationequipment at station A comprises in addition to relays .l-L, l-L-l and l-OL,

slow-to-release relay |--L-2, and relays l-S and I Si. Also at station A are two timed e1ay;-or timer,-circuits comprising vacuum tubes ;;I.V-*l:;a;ndrl-+V2, respectively arranged to become conductive in fifteen seconds and twenty- -;fivev seconds, and; a,,group of alarm relays l-A, 15

:for-iurnishing various alarm signals for the differenttests that may be made as hereinafter described. Start-stop switch H6 and tape switch J33, ;vwh'en operated, jointly serve to condition rotary distributor H35 for operation.

v.Inll'ign2, stationB comprises a typing-reperto- .rat.or..2;i Lfor receiving at station B :both incoming and ,.outgoing messages and for both Y printing .and:.perforating both the transmitted and the received messages on-tapeifll and a transmitterdistributor 254 ion translating each signal com- ..oination in another anessage perforated on a second. tape, such asta-pe 293, into a coded signal current combination for transmission oventhe five selective segments of start-stop rotary distributors2fl5, to conductorizfldthrough one or rmorerepeaterstoconductor Hit of: the normally closed line. circuit extending to-stationA. The

typing-reperforator Zllhrnay be of the type dis- -,closediin .Swan, United States Patent 2,308,554,, supra, and: the transmitter-distributor 2,055,567,:supra. Distributor 2435 in its idlecondi- .tion connects conductor 2% to a circuit extend- 240' unentaconductors 2,3! and 209, through the lower ing over .its :innerring brushes and stopsegwinding :of relay ;2,L, conductorfldcontact and uppenarmatureof relay :2-OL, to grounded positive :batteryJZI I. :Relay *2L: is one of two polarized relays, the other :beingrelay 2-L-l, ,which are @alterna-tely operated in response to signals incomingan d outgoing over the line circuit. :Thetranslated signal combinations at station Bxtnansmittednover conductor 20B cause'the operation of printer magnet i2-'-'1R, provided i or operating typing-reperforator 2M to produce a home, or.local,.copy of the message'transmitted :to station A. Powerswitch 2|2 serves to start, in operation, motor::2 3 for transmitter-distributor 294 and mot-or 2H for typing reperforator r20! :as well as the -station equipment at each of stations Band A. The operation of the station equipment at station B- is eifective to make ready-fo r-service tests'at each station in response-to'the operation of the powerswitch at either one ofthe stations. The so-called station equipment of station B comprises in addition to relays 2-L,-2.-=l ,--I, and 2-OL, sloW-to-release relay.2L--'2 and'relays 2 --S-| and 2S. Also at station Bare two time-delay, or timer, circuits comprising vacuum tubes 2V-l and 2-V-2 respectively arranged to become conductive in fifteen andtwenty-five seconds after ground connections are removed from their respective grid elements, and a group of alarm relays 2- A,

for furnishingvarious alar-msignals for the different tests that may he made as hereinafter desc ibed, Start-stop switch 2 L6 and tape switch 233, when operatedijointly serve to condition for operation'rotary distributor 205. g

' 'A general description of the operation of the apparatus atstations'A and B follows. Operation at stations AIand B .will be hereindescribed as they alternately occur in response to (1,) a call originating at station A and (2) a call originating atstationB. L

M Station A t When stationA is in=its open condition; motors H3 and 4am not operating, the filament circuits of the Vacuum tubes ;|V I and l-V-Z in, the time delay circuits are not energized, the

grid circuit of vacuum tube 'l--V-l is connected to ground at armature No. 2 of start relay l-P and the grid cincuitofvacuum tube |-V-2 is connected to ground at -the contact and inner upper armature of relay l S sothat should the filaments ofthe twotubes becomes energized, the tubes will remain non-conducting since their respective grids are connected to ground.

Station B Likewise When station Bis in its open condi tion, motors H3 and 214' are not'operating, the filament circuits of vacuumtubes 2--V-I and 2V2 in the time delay circuits are not energized, the grid circuit of vacuum tube 2-V-I is connected to ground atthe' outer lower armature and contact of relay 2 Sj-l and the grid circuit of vacuum tube "2V --j2 is connected at armature No. 2 of relay 2,-P so thatshould the filaments of the twotub'es. become energized, the tubes would remain'non-conductive since their respective grids are connected to ground.

3 Station A At the start of operations the attendant at one of the stations, say station A, requests, over an order wire that the power switch at station B be operated to its on position. .When power switch H2 at stationlA, which like that at station B is in its off position, is operated to its on position, two circuits are closed, one at its upper contacts for connecting source .I I5 of alternating current to motors H3 and H4, whereby both motors start operating and theother at its lower contacts for connecting ground to the operating circuit for start relay l-P whereby relay I-P operates. Relay I--P, upon operating, performs the following functions: (1) closes ,at its armature No. 4, a circuit whereby the filament circuit for vacuum tubes ,l-VI and I-V2 becomes energized, (2) closes at its armature No. 3, a connection in a circuit forfconditioning transmitterdistributor I84, that is; relay ITD, for operation, the latter circuit being capable of operating only after the transmitter-distributor start-stop switch H6 is operated to its closed position, (3) opens at its armature No. 2, the circuit connecting ground to the grid of vacuum tube lV--I whereby the vacuum tube is free to become conductive and 1) connects at its armature No. '1, grounded battery H1 to a circuit having paths for operating relays I-S-I and l-S but the latter relays do not operate until after vacuum tube IVIbecomes conductive to causethe subsequent release of the normally operated slow-to-release relay I--L-'2 aswill be hereinafter described. I i When ground at the-No. 2 armature of relay IP was removed from the grid of vacuum tube IVl, the ,potential' at condenser I'I-8 starts to and continues to rise and when such potential reaches a predetermined value, say after an in- .6 terval of fifteen seconds, the vacuum tube becomes conductive and relayl-O operates. Relay IO, upon operating, closes an operating circuit for relay I-OL which operates to send to station B an open pulse, referred to herein as a test, or check, signal. Relay I--OL, upon operating, opens the normally closed line circuit which extends through the lower winding of relay |L, the opening effected being for an interval of longer duration than that of a transmitted teletypewriter signal combination. Relay IL, under the influence of the biasing current flowing inits upperwinding, operates, causing its armature to move from its right-hand, or marking, contact, to its left-hand, or spacing, contact. Relay l-L, upon opera-ting, away from its marking contact, disconnects grounded battery H9 from (1) the operating circuit for printer magnet l--TR which momentarily releases and (2) the lower winding of'relay ILI and relay ILI under the influence of the biasing current flowing in its upper winding, operates to cause its armature to .move from its right-hand, or marking, contact, to its left-hand, or spacing, contact. Relay I--L-I, upon operating away from its marking contact, opens the operating circuit for slow-to-release relay I-L- 2 which after an interval longer in duration than that of a teletypewriter signal combination, releases to connect ground at its outer lower armature to a back contact and thereby completes the operating circuit for relay lS- I which operates. The latter circuit may be traced from ground at the outer lower armature and contact of relay l-L2, conductor I20, make-before-break contacts I21, through the winding of relay lS--l, resistance I22, conductor I23, armature .No. land contact of start relay I"-P,-to grounded battery I IT. The connection of ground at the outer lower armature and contact of relay I.L--2 also closes a second circuit which, at this time, shunts the winding of relay |'S, the shunting circuit being traceable over conductor I23,-resistance I24, conductor I44, back contact and outer upper armature of relay [-8, to the ground atthe outer lower armature of relay lL-2. I

Relay l--L-|, upon operating, to its left-hand, or spacing,position, closes an operating circuit for relay l -A which operates and connects ground through its contact and right armature, to conductor I25 to maintain' vacuum. tube I-V2 non-conductive after relay lS-l opcrates. Relay I S-l, upon operating, performs the followingfun-ctions: (1) closes at its inner upper armature and contact a locking circuit for itself and prepares an operating circuit for shunted relay l+-S whichwill not operate at this time, (2) removes ground at its outer upper armature and contact from the grid of vacuum tube l--V--2 and condenser flfi', but the substitute ground is maintainedlat the operated right-hand armature of relay l--A to hold' vacuum tube l--V-2 non-conductive at this time, (3) at its greases winding: tothereby causeirelay l n tooper e. ack; to its ri ht-nan.slum":v mar ei po ition 1 d, relay l-le-L with current again flowing in-its lower -w-inding, likewise operates to, its righthand, or marking, position. Relay l,-l' r,l, upon operating; to-its= marking position, (1-) closes the operating; circuit for slow-to-releaserelay lL,-2,which reoperatesto remove-at its outer lowerrarmature and contactthe ground for the shunting 'circuit for relay-l-S-which now operates anditomaintain closed at its inner lower armature 1 and: front contact the normally I closed operating circuit for printer magnet ITR whichis-normally energized, and (2) opens the operatingcircuit; for, relaylA which now releases: Relay IS, upon operating, (1) transiers at itsouter upper armature the lowermost contact of? relay; |L--2, from its back to its front; contact,(-2 disconnects at its inner upper armatureand contactthe ground connection from-the:oircuihextending over the contact and outerupper'armature of. relay; l-Si to the grid; of vacuum tube I.V---2, whereby a timing interval for-making vacuumtube l-V-2 active begins, but is not necessarily completed unless a failureoccurs, and (3) opens at its outer lower armature andcontact. another point in the operating circuit-for relay l--TD, the other point still opendn the operating-circuit for relay |-TD being at the; outer lower armature and contact of operated relay I--S-l-. Relays IS and l--S I remain'operated by means :of the locking circuit for relay l,'S--l'.

Station B3 Switch '2l2 at station B, upon being operated to its on position, closes (1) at its upper contact a circuit for connecting source-215 of alternating current to the-parallel paths extending to motors 2l3 and'2'l4; respectively, (2) at its lower contact an operating circuit for start relay 2-? which operates. Relay 2-P, upon operating, performs the following functions (1) closes at its armature No, 4, a path for energizing the filament circuit of vacuum tubes 2-V--l and 2- V2', (2) closes at its armatureNo. 3e, connection in a circuit for conditioning th transmitter-distributor 264, that is, relay 2TD, for operation, (3) removes at its armature No. 2 the ground connection from the grid of "vacuum tube 2-V-2 and condenserZZB whereby condenser 226 may begin charging to a value sufficient to make vacuum tube '2-V2 conductive, the interval of time required being 25' seconds or some other interval of time that may be determined, and (4) prepares at its armature No. 1 a circuit having operating paths for relays 2S--|. and 2S.

The open interval, or pulse, which originated through the operation of start switch I I2 at station A as previously described, is received at station B over the line circuit which extends over conductor I06, middle ring, brush and stop segment of distributor 205, conductors 201 and 209, through the lower winding of relay 2-.-L, conductor 2H1, contact and upper armature of relay 2-OL, to grounded positive battery 2| l.

The open interval in the line-circuit is efiective to cause relay 2L under the influence of the biasing current iiowingin the upper winding, to operate and thereby move its armature from its right-hand, or marking, position, to its left-hand, or spacing, position. The armature of relay 2L, upon being moved away from its marking contact, causes 1) printer magnet 21.T R= to release for short interval, of, time 7 as will be heremaiter (18-9, scribed, and (2) relay. z rLr-w-l to wbe oontrolled bythe biasing. current inits upper winding and the armature of relay 2,,L-r-l moves; iromdts, right-hand, orv marking, position to its, leftshand or spacing, position. Relay.2 L.l, upon operati-v ing; to its spacingpos-ition, causesrelaib 2.-- A,;to, operate and to thereby substitute grounifor, pre-. venting the chargingofcondenser 226 at this time to maintain vacuum tube 2V2 non-conductive. Also relay 2-'--Ll upon openingthecom nection betweenits armature and markingcgntact, permits slow-to-release relay 2'-I.+2to release after an interval slightly longer in duration than'a teletypewriter signal combination; Relay I 2;-L2 upon releasing, (1) disconnects at its Relay 2-S is shunted by the latter. path, and,

therefore does notoperate atthis time. Relay 2-S -l operates andlocks in a. circuittraceable to ground. at its inner upper armature andcontact.

The ground connection for the locking circuit now prepares an operating ground for relay 2S' which asjiust stated does not operate at this time because of the shunting circuit to ground at the outer lower armature and contact of relay Z-L2. Relay 2- -S upon operating, further functions to (1) connect in part at its outer upper armature and contact, a path to the grid of vacuum tube 2V.2 to maintain, the 25-second time delay circuit inactive; (2)" closes in part at its inner lower armatura theoperating circuit for relay 2,--TD, which cirouitwhen relay 2 -S later operates extends over the contact and lower armature of, relay 2'S; and; (3) removes at its outer lower armature ,andcontai t'the groiirndlconnection from the grid of vacuum tube When the line recloses because of. the release of relay IOL at stationA, the lineourrent then flowingthrough the lower winding of relay 2.L predominates over the biasing. current, flowing in the upper winding to thereby cause relay 2l.. L to return to its right-hand, or marking, position so that relay 2- -L- with current again flow,- ingin its lower winding, likewise'retumsto its right-hand, or marking, position. Relay zr 'LF-l, upon operating, to its right-hand, or marking. position (1) closes th operating circuit for slow;- to-release relay 2L2v which now reoperates (alto remove at its outer lower armature and contact, the ground connection from. theshunting circuit for relay 2-S so that relay, LL-+3; 12: erates; and (b)- to maintain closed, at, its. inner upper armature and front contact the normally closed operating circuit for printer magnet Zr TR which is; normally energized; (2)v opens, its left-hand, or spacing, contact, the operatingciruit for slowo-r le e reMv-Z-A whicliznowmee leases removing; ground at: ts: contac andz zishtw 4 positions.

the line circuit to end the open pulse transmitted to station A. Relay 2LI, upon returning to its normal, or marking, position permits relay 2-V--I inactive.

9 hand armature from the grid of vacuum tube 2V-2.

Relay 2 S, upon operating, (1) prepares at its outer upper armature and front contact a path ferjshunting relay 2--S-'-I when slow-to-release relay. 2L2 again releases; (2) connects at its inner lupper armature and front contact the ground connection to the grid of vacuum tube 2-V2 whereby the tube is maintained nonconductive; (3) closes at its lower armature and contact, the operating circuit for I relay 2--TD which operates providing start-stop switch ZIIi is in its on position; The attendant at station B now has access to the line for transmitting messages to station A. 7

However, if start-stop switch 2I6 is not in its on position, relay 2-TD will not operate to give transmitter-distributor 204 access to the line for message transmission purposes, and therefore 'no ground connections are at this time applied to the grid of vacuum tube 2-V-I. At the end of the fifteen second interval of no-grounded connection, vacuum tube 2V-I becomes conductiveto operate relay 2-0 and relay 2-OL is an sequently operated. Relay 2-OL, upon operating, opens the line circuit and an open pulse is thereby transmitted back to station A. The open pulse returned by station E causes relays2-L and 2-+'L-I to operate their respective armatures to spacing positions, as hereinbefore described. Re-

lay 2-LI, upon operating to its spacing position, causes (1) slow-to-release relay 2L-2 to release; and (2) relay 2--A to operate. Relay 2-.-+L-2,upon releasing at this time, completes the. shunting path for relay 2 S-I, which re- ;leases, the shunting path having previously been prepared at the outer, upper armature and front contact of relay 2-S. Relay 2--S--I, upon releasing, (l) disconnects at its inner flipper armaa of .relay 2-L--2 (2), opens at its inner, lower armature and contact,.the operating circuit for relay 2--,TD therebylocking-out the transmitterdistributor 204; (3) connectsground at its contact and. outer lower, armature to the grid of vacuumtube 2.V- I which becomes non-conductiveto causethe release of relays 2--Oand 2-.-;-OL, in turn, and the return of relays 2L and 2--.L-I, in turn, toatheir normaLor right-hand, Relay 2--0L, upon releasing, recloses 'outerlowertarmature and contact the holding ground for relay 2-S which now releases. Relay 2--S, upon releasing, connects a second ground at its inner upper armature and front contact to the grid of vacuum tube 2 V.-.-I' to maintain tube The receipt at station B of message signals transmittedfrom stationA, when station A has access to the line, operates relays 2-L and 2--L-I accordingly and slow-to-release relay 2'A opcrates. 'Ihe steady ground connection at the right-hand armature of relay 2A,-maintains vacuum tube 2V2 inactive. At the same time,

vacuum tube '2,-V--I is maintained inactive by the normal ground connection restored bythe release of relay Relay 2 L-- 2 being of Station A The receipt at station A ofthe return open pulse fromstation B operates relays IL and l.--LI to their respective spacing positions thereby operating relay I-Aand causing normally operated slow-to -releas relay [|L-2 to release. Relay IL2, upon releasing at this time, closes at its outer'lower armature and contact a circuit extending over outer upper armature and front contact of. relay I-S,' resistance I22, conductor I23, armatureNo; 1 andcontact of relay I-P, to grounded battery II! which circuit forms a shunt around the winding of relay I-S-I which releases. vl Relay ISI, upon releasing. (1) closes at its outer upper armature and contact a circuit,- in part, for making vacuum tube I -V--2 non-conductive; "(2) transfers, at makebefore-break contacts I2I, the operating path of relay IS to a holdingpath extending to ground at the contact andouterlower armature of relay I'-L2; (3) closes at its inner lower armature and contact the operating circuit, in part, of relay I-TD and (4) closesat its outer lower armature and back contact a circuit, in part, for making vacuum tube I-V-..-I non-conductive.

The reclosure of the line circuit due to the subsequent release of relay '2--O'L.at station E causes relays l-L and I'L'I tomove their armatures to their: respective right-hand, or marking, positions and relay I-1L--2 subsequently reoperates. Re1ay:I-L-2, upon reoperating, (1) transfers at its innerilower armature and contact, the operating circuit of printer magnet I-TR from groundedbattery I21. togrounded battery Ill], (2) removes at its outer lower: armature ground from the holding path for relay I-S which releases. Relay I.,S, upon releasing, (1) connects atlitsinner'upper armature and contact the ground 'c'onnectionto the circuit previously closed," in "part, at the outer upper armatureand contact of relay I.S-.I for making vacuum tube I-V--2 non-conductive and .(2) closes at its lower armature and contact the circuitfor operating relay I-TD when .required, the latteroperating circuitbeing traceable; when rclosed, from grounded battery at the armaturexand contact of relay I'--'-A-4, contact and armature No. 3 of: relay l-P, inner lower armature and contact of relay I--S.I, contact. and lower armature of relay I-S, lower armature and contact of relay I OL, conductor I29, through the-winding of relay ITD, switch II6'in its alternate, or operated, positionflto ground at contacts I30 of sixth pin I3I. The sixth pin I3I is normally in continuous engagement I with the runperforated part of the moving gtape=l03 but should the tape breaks apartor its supply at transmitter I40 becomes exhausted, then r pin I3I automatically moves in the direction thatjcauses contacts I3Il to open and therebystops the rotation of the brushes of distributor I05. 7

Relay ITD, upon operating, closes at its lower armature and contact a circuitfor operating start magnet I-ST--MG, the circuit being traceable from ground at contacts J32, tape switch I33,

contact and lower armature of J relay I-i-TD, through the windingof start magnet, I;'ST.MG, to grounded battery. Relay I-"I'D,-upon operating, also connects at itslupperiarmature and contacts. ground connection to the grid ofyacuum tube I--.V-I and the tube is maintained noninsists oted lever I34 from engagement with the locking cam I35, and shaft liifiunder the influence of motor H3, friction clutch, 1-31,.worm. I38 and worm gear I39, starts ro-tatingtopmove. the brushes of distributor l05pover; the distributor segments as well known in the art.

7 stations Mind's 'The transmitteredistributor... 1-04 .is controlled by friction clutch 131, worm L38, gear I39, shaft 136 and Istopcam I35; transmitter-distributor 204 V is shown operated in a similar manner except that it is controlled ibyfriction clutch 23],;worm .238, gear 239, shaft 236 .and.:stop ficam 235. Typing reperforators .Hll and 2M halve motorstwhich are running continuously from the time that their respectivepower switches are in their on positions but th'eperforatin printing and tape advancing operations are effective only whensignals are being receivedby the printer magnet, such as that designated .l--TR at .station A and :2-TR. at

station B. y

Transmission in message The message transmitted "at station A causes relays IL' and I'--I..'-'-'-l .to follow the signal impulses and relay lfL'2 being or the slow-torelease type remains in its normally operated position during message transmission. .Relay |-'L, upon -follow-ing the signals, causes printer mag-net l-TR to operate accordingly andgto Relay l'-Aat station and relay 2' "A at station B operate inli'esiionse to the bperati'on bf relays ll.'r''1l and I, respectively, but beingrof the slow-release type do not .releaseii during .the time the :niessa'ge is beingstransmitted over the .line circuit. Grouiiuiistherefere maintained connet'ed to the-grid of. each .or .rvacuum tubes 'I'V2 an d-"lbv-a-i .to'prevenit their respectively associated 25=scond time delay, oftimer, circuits from, :operating, .Eheground {atj-the upper armaturelof relay jfiflD atthis time in an 'operated positiong-is connected ina circuit extending over the. hack contabtand outerv lowerarmature of .relay. .lrI-Sfl at thistim-eiin a released position, to. the grid ofhvacuum tubal-V1]. and

therefore the...15 -second, tim r. circu t. at; station A. is. prevented r m o e ti .d ri amessas transmission from ,;Stat .On. A-..L. wfllbanot that when station. (Bis receiving theitr n mitie distributor 2041s, lock d. outgby the ,open condition of the operating circuit for relayi- -TD.

Transmission of n-siaye siasbnh siesta A The message transmitted "from station B causes relays '2Land 2-L'l to follow thev si nal impulses transmitted by transmitter 240 during the time 'thatdistributorioi isbperat'ing, but

relay 2-'L-2' being of the slow-release type, re- I mainsin. its normallyoperated position. Relay 2-"L, upon following the signals, fcauses printer magnet 2'-TR to operate; accordingly and to thereby produce in tape 202 a home, or local,

copy of the message transmitted from station the copy being in both perforated and printed for-m transmitted message signals. Y

ing at station A -oy eir the lih e an "f time distributor I-OS-is not operating loause .r ays I L and .l'-L- l to renew ng; incoming but relay l-L2 does notiesp nd, V eadreingly, t er i e m me fi f i- ,nals repeated by relay l- L' to atomic; ontal I102 both the perforated and prim'edeopy DI tfie message. Relay 15A {at station A affidrlayfi-A at station E operate in response to the operation of relays lL--l 'andl2''.l .-l. respectively but being of the slow-release type so net Tr ing the time the message is being transmitted and received. over the: line circuit. The grou d connections at the right-hand antennas of relays IA and 2-A aremaintai'ned connecte to the grids of Vacuum tubes l Y"2 Z"V;Z to prevent their respectively, associated 25-se";; 'nd delay. orti mer, circuits rroin op rating, -YIh e grams at thec uterlower arma ur ar, z sfi, at this time in ia .r'ele e jpo connected to th'e'g rid or vacuum tube and, therefore, the lfifs'cohd "tiih'eicir.

tion .13 reven ed from operating durm" mes sage transmission from station B fit l'iyill be noted that when station A] is reeeiv nggitr n rnitter distributor 'Ifol s iok out y the 29% conditionoi the operatingcircuit "for relay I TD.

Description "of tests Teddy foq'- semester WI'i'enit "ise'esi red to place the system i speration; the operation at either station A 'or statibn [B is area by operatin'gthe local power, or start, switch "its" position nn"-d atthe same 'tim ea request is made over anorder, or Gal-l, wire to operate to its "fbnf'po'siti'on, the power, or *st'artfswitc'h'at the "opposite station. However, by 'prear r ngemem the start switches at the two stations may be operated "at the i'same in sub- "saiiti ally "the same time. 'nlsb'the single :pole, Single throw switches "dte'a'ch station, as switches '1 is and 133 at station '1} and switches 2 li ai ifd '2 33 at station '3, are bperated their respective cl osedipesitions, that-is, if "both statiohs are prepar'edt b transmit messages. I 'Assume'th'atthe o 'rator at station "initiates ja 'call to station B; power switch 112 atstation''A and power switch 212"21.stationB are'pperated to their respective on positions; "station A power switch 112 "upon "being sperm-ed; 'I'closes (1') at its upper. contents a'circurt for operating m'otors 114' and I I5 and Both motors startbpen atingand (-2)""at"it's lower contacts, closes an 'operatingbircu'it for r'laVk-Pwhichoperates to start "the 'iuz'iction's of initiating the call to "sta- "tion B. 'Relay 'u'pon operating, :11) closes at its No. 1 'a'rimatureacircuit: Iorenergizing'the 1filainent"circuit of vacuum tubes i--TV-Ffffllfld l- -V-2 which iare'i now' in condition IOZfbCOHl- 'i'ng eohductive except"forrgroundedtgrid elements, (2-) closes "atitsiNo. 3arxhature acircuitextending from grounded battery I4 I, right-hand armature and :contact of; relay l-,-A l, -contact*and armatureNo. 3 of relay -l-P,;inner "lower1armature and contactcfrelay l.;S 'l.,""contact and lower armature of relay l sglower armature and contact .TOf relay l OL, conductor J29, through the winding of relay -I- -;TD -start stop xswitchgllfi in its closed position ifistati nA is prepared to'transmit a message to station B contact I to ground; and relay I T9 op rates to make j the, transmitter-distributor; {0Q accessible to the line circuit extending to station B,

13 (3) opens at its No. 2 armature the ground connection normally connected to the grid element of vacuum tube I-V-I and grounded. battery I42, and condenser I I8 therefore begins to charge to a value approaching the potential of grounded battery I42 and (4) prepares at its No.1 armature a circuit extending over conductor I23 and then through parallel paths one extendin through resistance I22, winding of relay ISI, normally closed make-before-break contacts I2 I, to the open contact of the outer lower armature of relay I-L2, and the other extending through resistance I24, back contact and outer-upper armature of relay IS to the open contact of the outer lower armature of relay I--L2. However, the ground on the contact andupper armature of relay ITD in its operated position maintains inactive the vacuum tube IVI thereby preventing the 15-second timer circuit at station A from operating during the time that transmitter-distributor I04 is sending a messageto station B.

Should the start-stop switch IIG be operated to the open position to resume thetransmission of test signals from station A, relay ITD would release, removing the shunting ground at its contact and upper armature. After fifteen seconds, condenser I I8 charges to a predetermined value that is sufficient to cause vacuum tube i-V-i to become conductive, or, active, and. relay IO consequently operates. Relay IO, upon operating, causes relay IOL to operate, thereby opening the line circuit, and looks out relay I-TD, that is, it prevents transmitter-distributor I04 from operating. The opening of the line circuit by relay IOL allowsthe biasing current in the upper winding of relay I-L tofmove the armature ofthe latter relayfrom its marking, or right-hand, contact to its spacing, or lefthand, contact and therefore grounded battery H9 is removed from the circuit of two parallel paths, one extending through the lower winding of relay IL-I whereby relay IL--I moves its armature from its marking, or right-hand, cont to its pacing, or left-hand, contact and the other extending over the inner lower armature and contact of relay l-L--2 and through the winding of printer magnet ITR to ground whereby magnet ITR releases. Printer magnet ITR releases for a short interval of time, as will be hereinafter described, as soon as the armature of relay IL moves away from its marking contact. The removal of the armature of relay IIr-I from its marking contact, opens the operating circuit for normally operated slow-torelease relay I--L--2 and after an interval of time having a duration slightly longer than that required for the transmission of a start-stop teletypewriter signal, relay IL--2 releases and thereby connects grounded battery I21 over the make-before-break contacts I28, to the operating circuit for the printer magnet I -TR of the reperforator IOI and the printer magnet I- TR is restored to its normally operated condition, the interval of time during which printer magnet II'R is released being slightly longerthan that required for the transmission of a start-stop teletypewriter signal.

Relay I-L--I, upon moving into its spacing, or left-hand, position, causes alarm relay IA to operate and to thereby add another ground connection to the grid element of .vacuum tube I-V,2 and grounded battery I43. Vacuum tube I--V2 at this time is prevented from becoming conductive during the time, that relay operated. a

Relay I-L,-2, upon, releasing, closes at its outer lower armature the ground connection to the parallel paths hereinbefore described and relay I- -S-| operates, but relay IS is shunted by conductor I44 and therefore does not operate immediately. Relay I--SI, upon operating, (1) connects at its outer lower armature and front contact the ground connection to the grid of vacuum tube I-V--I and grounded battery I42,whereby vacuum tube IV--I returns to its non-conductive state and relays I--O and I -OL release, (2) closes at its inner upper armature and contact a locking. circuit for itself and ,(3) opens at its outer lower armature and contact a second point in the operating circuit for relay l-TD to maintain transmitter-distributor I04 in a locked-out condition. Relay IOL, upon releasing,,recloses the line circuit and thereby causes both relays I--L and I--L-I to return to.

their respective marking positions and relay IL-Z to its normally operated condition. Relay I-L-I, upon returning to its marking position, causes relay IA to release and thereby removes the ground connection fromthe grid o-f vacuum tube IV--2.

,Relay IL-2, upon reoperating, that is, returning to its normally operated condition, removes ground connection at its outer lower armature, from the shunt conductor I44and relay I-'S now operates in a circuit traceable through the locking ground for relay ISI. Relay I-,-S, upon operating, opens another point in the operating circuit for relay ITD as an assurance against the transmitter-distributor I04 operating at this time. Therefore with relay IA released, and relays ISI and IS in their respective operated positions, ground connections are removed from the grid of vacuum tube I--V-2 and condenser I26 is allowed to begin charging to a predetermined value from grounded battery source I43. In the event that the open pulse, or test signal, say of 0.326-second duration which is equal in time to two blank character signals, does not reach station B either because of a break in the line circuit, or that power switch 2I2 at station B is not moved to its operated, or ion, position, no open pulse will be received from station B and the failure to receive such line signal from station .3 allows condenser I26 to, completely charge to the predetermined value, say in 25 seconds, ,whereby vacuum tube IV2 becomes conductive to operate relay IAL. Relay IAL, upon operating, causes relay I-A-4 to operate. Relay I--A4, upon operating, (1) opens at its right-hand armature and contact, the operating circuit for relay ITD andtransmitter-distributor I04 thereby locks out of use, (2) closes at its inner left-hand armature and contact a locking circuit for itself, traceable over conductor I45, release key I46 to ground and (3) closes at its outer left-hand armature and contact a circuit traceable from ground, conductor I41, through lamp I48, through the winding of alarm auxiliary relay I49, to grounded battery and relay I49 operates. Relay I49, upon operating, closes, at its left-hand armatures and contacts, circuits for respectively operating audible alarm I50 and visible alarm lamp I5I. Alarms I50 and I5I,,furnish a major alarm which indicates that thesystem is not ready for service. At station E all the equipment does not operate in response to an incoming open pulse when switch 2I2 is in its off position. Only relays 2--L, 2-LI and of tape for the reperforator whereat th supply is low. For example, if the supply of tape on reel I54 becomes low or exhausted contacts I55 will close and complete an obvious circuit for lighting lamp I55 and operating relay I49. Relay I49 operates and as hereinbefore described, closes circuits for lighting lamp [i and ringing bell I50 to furnish the. necessary alarm or indication. The lighting of lamp I56 indicates the source of trouble.

What is claimed is:

1. A channel of impulse transmission having two stations intertransmissably related thereto, each having sending means capable of impressing impulses upon said channel andmeans capable of receiving impulses transmitted by the send ing means at the far station in combination with means operable, when neither of said sending means is so impressing impulses upon said channel, repeatedly to send test signals back and forth over said channel at frequent intervals, and means operable by failure of a test signal to arrive to indicate the defective condition of the channel. 1

2. A channel of impulse transmission with reciprocally operating, sending and receiving mechanisms at the terminals thereof for sending backward and forward over said channel a series of test signals, with means immediately responsive to a complete test signal incoming over said channel for, conditioning the mechanism receiving the completed test signal tosend another complete test: signal over said channel in the opposite direction, and means for automatically repeating said reciprocal operation at regularly recurring intervals. I

3. A telegraph system comprising a channel of transmission having associated therewith two automatic storage transmitters at geographically separated points, each of said transmitters having a start switch, an automatically operating timing means at each point, and means at each of said points operative in response to the operation of its local one of said timingmeans for controlling the other of said timing means over said channel whereby first one and then the other of said transmitters is given access to said channel upon the completion of one or more messages transmitted successively over said channel when its start switch is closed.

4. A telegraph system comprising a channel of transmission having associated therewith two automatic storage transmitters at geographically separated points, an automatically operating timing means at eachpoint, each of said operating timing means includes other means for sending over said channel in one direction an impulse at regularly recurring intervals of time, each of a predetermined duration, circuit means at one of said points responsive to the completion of an impulse sent'from the other of said points for automatically seizing said channel for message transmission to the other of said points, other circuit means at the other of said points responsive to the completion of an impulse from said one point for automatically seizing said channel for message transmission to said one point.

5. A telegraph system comprising a channel of transmission having associated therewith two automatic storage transmitters at geographically separated points, an automatically operating tim ing means at each point, said operating timing means including means operable at regularly recurring intervals of time only at such times as when no message signals are being transmitted in either direction oversaid channel or prepared for transmission, to send a test signal intermediate other test signals received from the other separated point, means operable at the above-mentioned times to alternately lock said transmitters against transmission of message signals, and other means controlled by each of said timing means during the locked out intervals of its associated transmitter for preventing the reception of'message signals.

6. A telegraph system comprising a channel of transmission having associated therewith two automatic storage transmitters at geographically separated points, each said transmitter having a start, switch, automatically operating timing means at each point, each said means controlling the otherover said channel whereby first one and then the other of said transmitters is given access to said channel if itsstart switch is closed, and means operative by one of said transmitters seizing said channel during a period wherein it has access to said channel to suspend. operation of a t min mea d r nsth o u n transmission by the seizing transmitter. I

7. A telegraph system comprising a channel of transmission having associated therewith two message signal transmitters at geographically separated points, each said transmitter having a start switch, a plurality of automatically operating timing means of difierent operating time intervals, ateach separated point, one timing means at each pointhaving means for controlling its associated timing means of different time interval at the local point and said plurality of timing means at the -distant point, testsignaling means at each .separatedpoint responsive to the operation of its local said onetiming means foralternately transmitting over said channel at recurring intervals a test (signal, test signaling means including means operable depending upon the duration of operation of itslocal said one timing means for allowing local one of said transmitters to seizefor a predetermined interval of time the channel tor message signaling purposes, other operable means responsive to a test signal incoming over said channel for releasing the local said one timing means and lockingout said local one transmitter, still other means responsive to the release of saidoperablemeans for causing the local operating timing means oi. Lsaid difierent operating time to start operating, and alarm means responsive to the complete operation of said local operating timing means of said difierent operating time tor indicating that trouble exists in the system.

. 8. A signal transmission system comprising a plurality of stations, message sending and message receiving means at each of said stations, an impulse transmission channel interconnecting said stations, each of said stations having test signal sending means for impressing open impulses on said channel alternately as between said stationsat regularly recurring intervals of time and test signal receiving means for receiving said open impulses transmitted over said channel from the other of said stations. when said message sending means atbothl of said stations are idle,

and alarm means automatically operative when said channel remains closed for a prolonged period of time toindicate. a defective condition of said channel. a I

9. A signal transmission system comprising a plurality of stations a transmission channel interconnectingsaid stations, transmitting and distributingmeans at each ofsaid stations for trans- 19 mitting messages over said channel, means at each of said stations for receiving -m'essages transmitted over said channel 'from another ef said stations, meansfor automatically transmitting test signals over said channeL'fir-st from-the call originating-one of said-stations andthen from the call terminating oneof said stations during the time-that thetransmitting and distributingmeans at the call originating stationis idle but in a condition for transmission over said channel, andmeans for disabling thetransmitting and distributing means 'at saidcall originating station when a test signaltransmitted in either direction over said channel is not received. 10. A signal'transmission system comprising a plurality ofstations, a transmission channel interconnecting-said stations, transmitting and distributing means ateach oi said stations for transmitting messages over said channel, means at each of saidstations for receiving messages transmitted over said channel, a 'swi'tch at each of said stations for conditioning "for operation its local one of said transmittingand' distributing means, means for automatically transmitting test signals over said channehfirst from one of said stations and then from the other of said stations during the time-thatsaid switches areintheir operated condition, and -means at eachof said stations responsive to a test signal-incoming'oversaid channel when theswitch at one only-of -said stations is not in its operatedposition, for indicating that said one only switch" is not in its operated position; 11. A signal transmission systemcomprising a plurality of stations, a transmission channelin- 'terconnecting saidstations, transmitting and distributing means at each ofsaid stations for transmitting messages over said channel, means at each of said statio'ns'for receiving messages transmitted over said channel", a*"s'w itchateaohof sai'd stations for conditioningfor' operation its local one of said transmitting and distributing means, means for automatically"transmittingtest signals over said -channel,ffirst"from"one of said stations and then from the other of said stations during the time that said switches-are 'in their on positions, and means at each of said'stations responsive to a test signal-transmitted from one of said stations when'the'switch at said'orie station is not returned to normal at the time the-switch at the other of said stations is restored to normal, for indicating that said switch at 'saidone station is in its 'ofi-nonnal-position.

12. A signal transmission system comprising a plurality of stations, a transmission channel interconnecting said stations; transmitting and dis-- tributing means at each of 'said'stations for transmitting 'messages over "said channel, 'means at each of said stationsfor receiving messages trans mitted over said channeLa switch at'ea'ch of said stations for conditioning for-operation its local one of said transmitting and distributingmeans, means for automatically transmitting test signals over said channeL'first from -on'e'of said stations and then from the other-ofsaid stations during the time that said switches are in their on positions, and means'ateachof said stations responsive to a test signal automatically transmitted during transmission of a-message when one of said switches is inadvertently restored to normal to give an indication that said one-switch is in its off position;

13. A signal transmission system comprising a plurality of stations, a transmission channel-interconnecting said stations, transmittingand dis- 20 tributing means at each of said stations for transmitting messages .over said channel, 'means at each of said stations for receiving messages transmitted over said channel, a switch at each of said stations for conditioning for operation its local 7 one of said transmitting and distributing means, means for automatically transmitting test signals over said channelgfir'st from one of said stations and then-from the other of said'stations during the time that said switches are intl-ieir on positions, and means responsive to any defeet in the electrical and/or mechanical operation of any oneofs'aid transmittingand distributingmeans and/ or receiving means, effective to interfere withthe transmission ofls'aid messages in either direction, for automatically disabling said transmitting and distributing means at the sending station. v

'14. A signalitransmission system comprising a plurality of stations,- a transmissionchannel interconnecting said stations, transmitting and distributing means at each of said stations for transmittin messages over said channel, means at each of said stations for receiving messages'tr-ansmittedover said channeLaswitchat each of said stations 1 for conditioning for operation its local one at said transmitting and distributing means, means'forautomatically transmitting test signals over said channeL' first-from one of saidstations and then from the other-of said stations during the time that said switches or in their -on positions, and means :"controlled bysaid means for automatically transmitting test: signals for 2 preventing simultaneous sending from said plurality of stations. v

15. A signal transmission system comprising-a plurality of stations, a transmission channel interconnecting said stations, an operable switch at each ofcsaid stations for conditioning said system for -operation ,-'time delay means located at each of saidstationsandeach arranged to be conditionedfor operationin response to the operation of its locally associated switch, energy storing elements; in each of said time delay means for providing a predetermineddistinctive time interval before the efiective operation of each of said delay means occurs, a test signal transmitting means-atone of said stations effective I to transmit a test signal: of "a definite time duration over said channel in response to :the eflective operation of fits locally associated time delay means, other time delay means located at :each of said stations and each arranged'to be conditioned for operationinresponseto the operation of its locally associated switch, energy storing elements in each of said-other time'delay means, having .a predetermined :distinctive time interval before the effective operation of each of said other time delay means occurs, electromagnetic means at the other of-sai d stationseffective in'response to the test signal incoming oversaidchannel to preventthe operation ofthe first mentioned time delay means at said other station, other .Itest signal transmitting'means at the other of said stations efiectiveto transmit a return test signal of a definite time duration over said channel'subsequent-to the reception of the'first-mntioned test signal, the second-mentioned test signal transmitting-means-being operative in response to the operation o-f o-neof said other time delay means at theother of saidstjations, other electromagnetic means at said one station efiective in response to the secondamentioned test signalincoming oversaidchannelto prevent-the operation ofthe second-mentioned time delay means 21* at said one station, and alarm means at each of said stations operative in the event that the test signal incoming over said channel isnot received at the particular station to indicate that the system is not functioning satisfactorily.

16. In a communication system, a plurality, of stations each provided with an impulse trans? mitter and an impulse controlled receiver, a channel of impulse transmission for interconnecting said stations for twoway communication, one way at a time, test signal sending means at each of said stations for impressing open impulseson said channel at regularly recurring :intervals, test signal receiving means for receiving said open impulses transmitted over said" channel from the other of said stations when" message sending means at both of said stations are idle; means under control of the test signal sending means at both stationsfor permitting thertest signal sending means at said stations to alternately transmit an open impulse over said channel and other means responsive to an oiT-normal condition of said channel, such as remaining con tinuously closed or continuously opened, for furnishing an alarm at all of said station-s1 17. A channel of transmission provided at each terminus with means for sending message signals or check signals, means operative to time a period following the last transmission of either of said types of signal, and means operative dependent upon non-reception 'of any signal within the period to lock in a trouble condition. i

18. A channel of transmission provided atjone end with a transmitter operating under control ofstored message signals supplied at intervals as they become available; means operativ'e'to initiate transmission from said transmitter, timing means operative at the end of said trans mission to time a given period of timegpulse sending means automatically operative at the end of said period of time for sending an additional signal of comparatively long duration, a second transmitter operating under control of stored message signals as they become available and arranged for connection to the opposite end of said channel, means at said opposite end of said channel responsive at the completion of said additional signal incoming at said oppositeend for giving said second transmitter access to said channel for transmitting its stored message signals as they become available to said one end, other timing means at said opposite end operative at the end of transmission from said second transmitter to time a given period of time; pulse sending means at said opposite end automatically operative at the end of the second-mentioned period of time for sending to said one end a reply additional signal equal in duration to the first-mentioned additional signal, and means operative upon receipt of said reply signal within an extension of definite duration of the firstmentioned period of time for giving the firstmentioned transmitter access to the channel for transmitting other message signals to the opposite end, and so on indefinitely. 19. A channel of transmission provided with equipment in accordance with claim 18 at each terminus wherein the pulse sending means comprises a time delay circuit cooperating with message signal responsive means, aslow-to-release means non-responsive to message signals, and other means arranged to operate only in themterim between the start oi operation of said mess Signal n ve ansi re n e t a incoming, additional signal ,and the release: of

said slow-to-release means for initiating trans mission of messagesignals from the transmitter at the local terminus whereby'saidtransmitter at the local terminus has access to said channel for transmission at any time between the receipt of the last signal received atthe local terminus and the, transmission of itsnext outgoing additional signal, butinot thereafter; until a further additional or message signal has been received.

20. A communication system havingsending equipment at eachterminus of a channel of communication, means operative during an idle condition of said sending equipment to send a, signal including at leastapul'se from one terminus to the other, timing means at the sending terminus to count of! a predetermined intervalifollowlng the sending of said signal, timing means at the receiving terminus tocountuoif a time interval of shorter duration from the receipt of said signal and then send a return pulse, and means at sending terminus operative to inhibit transmission. over such system if the return pulse is not greceived prior to the expiration of the predetermined interval. 1 i i 5 21. In a system comprising a telegraphlchan nel provided with message transmitting equipment at a sending terminal, operating means for transmitting messages over ,said 'channel under controlof said equipment, supplemental means for sending a non-messageasignal: of one pulse only. at intervals upon cessation ofhoperation of said equipment to transmitmessagexsignals, a,

' trol of said equipment, supplemental means for sending a non-message signal ofionepulseonly at intervals upon cessation of operation of said equipment to transmit message signals, a'receiver associated with said channel at a remote point, operative to receive message signalsthereover and means operative upon failure to receive message signals thereover and means operative upon failure to receive messagelornon-message signals during a, definitely timed period. A a

23. In a telegraph system, a channel of telegraph transmission provided with means for sending message signals and operating means therefor, means for sending at regularly recurring intervals during the idle periods between message transmission periods ,atcheck pulse, means for automatically operating the thirdmentioned' means independently ofthe secondmentioned means, a recorder for receiving and recording said message signals, andmeans responsiverto each operation of the;-third-men.tioned means for operating said recorder, said recorder operating in response to each check pulse transmitted. t r

24. In a telegraph system, atwo-way channel of transmission provided with message signal sending means and operating means therefor at each terminus for transmitting to signal receiving means provided at the opposite terminus, supplemental means for sending at regularly recurring intervals during the idle intervals between selector.

23 message transmission intervals is "check pulse over said channel to .checkithe :operativeness and continuity of said channel, and means responsiveto-each operation of said supplemental means for operating said signal receiving means, said receiving means operating in response 'to eac h checking pulse transmitted and' received.

25. A signal receiving system having a selector operable to' make selections in accordance with permutation code, contact'means operable in response .to every selection by said selector, timing means for measuring off 'a predetermined time which is reinitiated upon every operation of said contact means, a circuit, and -means for closing said circuit operati-vely controlled by failure of said contact means to operate over a continuous period of time greater in duration than said predetermined time.: V

26. A signal receiving stat-ion comprisinga conductive path, contact means, timing means for modifying the conductive condition of said path upon expiration ofa given time interval during which said contact means remains unoper'ated,

and a permutation code selector, said-contact means being operative inrespon'se toeveryselec- .tion received over said path foi operat-ingsaid 27. A telegraph system comprising a channel of transmission, a machine sender-and receiving means at one terminal, sending means and receiving means at i the other terminal, said system and its transmission and reception equipment capable of assuming an idle condition, 'means operative during said condition for sending check or non-communicationsignals from one end of the channel to the other independently of the operation of said .machine sender .and receiving means at either terminal, -and"means automati cally operative for 'sendingrcheck or non-communication signals from the other end to the one end independently :of the operation of said machine sender and receiving means at either terminal, and means whereby :such signal sent from each such end controls the'transmissionof such signal from the other.

I 28. A telegraph system eomprisinga channel'of transmission provided at either terminus :wit h an automatic storage control transmitter, means including-pulse sending means at eitherterminus of the system and pulse receiving means responmentincluding a pulse sender .at-each terminus whereby first one terminus and then the other assigns atime in which transmission may begin by the other, means for preventing initiation of transmission at either terminus except within the assigned time andmean's effective-upon the beginning of transmission within the assigned time and continuation thereofiby the sender'at one terminus to hold' the channel available for continuedisending, all under control of {the trans mitting sender.

all

30. A telegraph channel oftr'ansmission hav ing means :ror transmitting pulses" from each terminus of the channel'"toward the other, means operative upon cessation o'f transmissionirom one terminus t'o'mea su-re a time interval Within which is. responding pulse sh'Ouldbe received, and me'ans operative upon fa'ilure to rece'ive {any respondinghpulse within "the measured time' interval to sound an alarm. V 1 I .31. ..A telegraph channel' of transmission having means for transmitt'ingipulses from each teroperative upon cessation of- ,transmis'sion i-rom one terminus to the other to'm'ea's'urea time."within whicha responding pulse. should bereceived; and means operative upon failure to rlecei-vefany responding pulsev within 1 thei-imeasure'd time interval to prevent further transmission away from said one terminus until .the' cause of failure to receive the responding slpulse ihas been rectified;

32. The method of reducing does or mutilation of messages transmitted over v.a system which includes a start-stop channel of telegraph tr-ansmission and automatic'transmitter means effective to transmit :thereover .fromtime to time-as stored message materialis supplied fto said'tr'ansmitter means to be jtransmittedwhich:comprises, upon said channel becoming temporarily idle as a result of cessation :of message'transmission by said transmission means, sending'pchecksignals from time to time'oversaid channeLreceivingsaid check signals at. the far end of said channel, receiving and verifyin'gthe receiptxof-said check signals by"-causingeach ofthemito control the sending of a conditioningnheck "signal back towardrsaid transmitter means, :ena'bling-finitiation of message transmission byzl said .transmitter means by said conditioning 'checkisignaL'and preventingthe initiation ofrnessage' transmission 1 by said transmission meansincidentxto: sending a check signal awaylfrom ituntil a further conditioning check signal is receive'duback' I 33;:A' telegraph system comprising normally energized line circuitv of 'impul-setransmission,

- reciprocally operating, sending :and receiving mechanisms at the terminals of said circuit ifor sending backward and forwardho'ver said channel aseries of test signals, means included Iinisaid line circuit immediate-ly 'responsiue tcaxcompl'ete test signal incoming :zoverfsaid circuit for :con'ditioning the mechanism receiving :the completed test signal to sendanother complete test. signal over said circuit ingthe opposite direction; and means .for automaticaly repea-tingsaid reciprocalopera-tion at regularlyrecurrin-g intervals.

E AR PRAIZNER. nEFnnsNoes-cirep i following i.'eferences are of record :i'nthe file .of this patent: 1'

UNITED STATES' smears. '1"

Number f Name 7 1 f "j Date] 1,904,618 Burton April 18, 1933 1,972,326 Sept; 4,1934 1,677,853 Dudley u1y1rz,ji92s 1,601,941 Clokey 'Oct; 5,1926 1,723,220 Thorp Aug 16,1929 1,324,798 r QCon'Way l3ec. 1,61 1919 1,747,321 m n -Feb.-;1s,193o 1,939,613 1 Watson'fl'. Decilz, {1933 2,003,325 Watson" 'June' 4,1935 2,332,645 Keithley o'ct.26,-1943 1,681,489 Locke Aug. 21', 1928 2,351,014 con neryn'un 'Jun"13,1944 

